1. Field of the Invention
This invention relates generally to saws for cutting concrete surfaces. More particularly, the present invention relates to powered, green concrete cutting saws that are used for crack control. Known prior art concrete cutting saws are classified in United States Patent Class 125, Subclasses 13.01 and 14.
2. Description of the Prior Art
It has long been recognized that to reduce cracks in concrete surfaces adequate control joints must be provided. Without numerous joints concrete slabs will crack like glass relatively soon after the onset of hydration and shrinkage. As the concrete surface continues to cure, it expands and contracts depending upon numerous variables. Virtually from the moment of pouring the contractor is under time pressure to begin "crack control." Control joints may be established in a variety of ways, but sawing is a preferred method. By establishing a plurality of longitudinal and/or transverse cuts, plastic concrete may be properly stress relieved so that unwanted surface fractures and cracks are minimized.
After pouring, and prior to cutting, plastic concrete is surface finished by appropriate power tools. Pavers, comprising one or more elongated, rotating tubes that traverse the span of plastic concrete, are commonly used with large pours in highway construction for surfacing immediately after pouring. Typically they are used out of doors. A smaller concrete job like a driveway might require only a floating finish with a light broom texture. Riding trowels, equipped with revolving blades or plans, are suitable for fine finishing plastic concrete on large floor jobs soon after pouring. As the freshly poured concrete "sets," it soon becomes hard enough to support the weight of specialized finishing trowels. While it is still "green" (i.e., within one to several hours after pouring depending upon the concrete mixture involved), power trowel pan finishing is recommended. Soon after panning, trowelling with power blades may begin as the slab adequately hardens. Numerous concrete finishing machines are known in the art. Proper and timely finishing insures that desired surface characteristics including smoothness and flatness are achieved.
Properly placed cuts in the concrete, usually about 0.75 to 2.5 inches deep, function contraction joints to reduce cracking. In effect, the contractor prevents the formation of visible concrete cracks by the sawing process, so the outer surface will be appear as unmarred as possible. It takes a rather large and heavy machine to cut hardened concrete. So-called "green" concrete that is just beginning to cure cannot support the weight of heavy machines (and the human operator) without surface marring and degradation. Further, typical machines require expensive diamond blades that must be lubricated during operation and routinely replaced. Although they work acceptably with rock-hard concrete mixes, when encountering green concrete the rotating blade may chip exposed, outer edges of the relief cuts, disfiguring the surface finish and appearance. To reduce spalling effects from conventional water lubricated saws, it is not uncommon to wait until the evening after pouring or the next day before stress cutting begins. Unfortunately, cracking may already have started by this time. Even if visible cracks have not yet formed, conventional rotary blade saws for cutting hardened concrete have several disadvantages. Typically they are big and expensive, and they require that the contractor return to the job site at a later time.
Consequently, various methods and devices for initiating crack control as soon as possible after pouring have evolved. These contemplate the surface cutting of green concrete. U.S. Pat. Nos. 4,769,201, 4,889,675, 4,928,662, 4,938,201, 5,056,499, and 5,086,750 are exemplary. These references broadly teach the sawing of relatively green concrete with lightweight, powered carriages that support a motor and an abrasive cutting blade. To reduce groove degradation with wet concrete, the blade is rotated to "up-cut" the groove. Further, edge regions of the cut made on opposite sides of the blade are directly contacted and temporarily reinforced by structure associated with the wheeled carriage. For example, the last mentioned patents disclose a slotted skid plate penetrated at least in part by the rotating saw blade. The skid plate distributes force to prevent surface penetration. It slides along the concrete and lends structural support, pressing down on the concrete immediately adjacent the groove edges to stabilize them during cutting. In an alternative design discussed in said references, a portion of the cutting blade proximate the stress relief cut is sandwiched between adjacent segments of a slotted roller wheel. The roller wheel segments press down upon opposite edges of the groove like the skid plate discussed previously. The slot is penetrated in part by the blade and generally aligned with the cut.
U.S. Pat. No. 3,663,060 discloses a wheeled saw ideal for extremely long cuts in hardened concrete. It discloses a wheeled carriage having a pivoted blade controlled by a remote handle. The blade is centered over the frame. The latter device is best employed upon large slabs that have substantially cured, like airport runways or the like.
U.S. Pat. Nos. 2,673,725, 2,700,256, 3,357,745, and 4,840,431 disclose large conventional saws disposed upon wheeled carriages. Blade control is effectuated by various diverse means of tilting the blade arbor and shaft.
Related prior art saws especially adapted for cutting green concrete were manufactured previously in small quantities by Allen Engineering Corporation, the instant assignee, under its former model numbers GM-150 and GM-400. Similar saw structure was first publicly disclosed in January of 1993. These designs feature a wheeled carriage comprising a partially encircling frame that pivots a captivated subframe. The motor and blade system mount upon the tiltable subframe for remote control by a rearwardly extending handle. Roller supports haphazardly extend exteriorly of the frame. A cooperating guide roller system includes slots penetrated by at least a portion of the up-cutting blade. Opposite, aligned segments of the guide roller contact the relief channel edges to resist spalling or cut deformation. Because of wheel positioning and unbalanced frame dynamics, the aforementioned saws are somewhat unstable. In operation, workers develop a habit of "fighting" these saws. Operator tendency is to overcorrect saw movement, which tends to vacillate about the desired straight cutting path. Stated another way, when pointed in a given direction by an operator determined to make a straight cut, these prior saws tend to migrate about the intended path in response to blade vibration, thus failing to make the best cut possible.
My new saw solves the aforementioned problems relating to instability. Unlike any known prior art green concrete cutting saw, it operates "squarely" with a minimum of corrective effort on the part of the operator. In other words, it is desirable to provide a green concrete cutting saw of the character described that cuts in a straight line without marring the surface finish, notwithstanding the significant vibration that ordinarily misdirects less capable wheeled cutting saws.